Electrode-Defined Unsuspended Acoustic Resonator

ABSTRACT

A bulk acoustic resonator operable in a bulk acoustic mode includes a resonator body mounted to a separate carrier that is not part of the resonator body. The resonator body includes a piezoelectric layer, a device layer, and a top conductive layer on the piezoelectric layer opposite the device layer. The piezoelectric layer is a single crystal of LiNbO 3  cut at an angle of 130°±30°. A surface of the device layer opposite the piezoelectric layer is for mounting the resonator body to the carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 16/037,499, filed Jul. 17, 2018, entitled “Electrode Defined Resonator”, which claims the benefit of U.S. 62/699,078, also filed Jul. 17, 2018, and claims the benefit of U.S. 62/860,426, filed Jun. 12, 2019, entitled “Electrode-Defined Unsuspended Acoustic Resonator”.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a bulk acoustic resonator and, more particularly, to a bulk acoustic resonator having a resonator body and, optionally, one or more connecting structures that can be used for supplying electrical signals to one or more conductive layers of the resonator body.

Description of Related Art

Radio frequency communications have progressed from “1G” system in 1980's, to “2G” system in 1990's, “3G” in early 2000's, to current “4G” system that was standardized in 2012. In current RF communications, the RF signal is filtered with surface-acoustic-wave (SAW) filters or bulk-acoustic-wave (BAW) filters.

Film-bulk-acoustic-resonators (FBAR) and Solid-Mounted-Resonators (SMR) are two types of BAW filters that are piezoelectric-driven micro-electro-mechanical-system (MEMS) devices that enable current 4G RF communications capable of resonating at a relatively high frequency with a relatively low insertion loss, as compared to SAW filter devices. These BAW acoustic resonators comprise a piezoelectric stack that includes, in one example, a thin film of piezoelectric material sandwiched between a thin film top electrode and a thin film bottom electrode. The resonance frequency of such piezoelectric stack is thickness-based or depends on the thickness of the thin films of the piezoelectric stack. The resonance frequency increases as the thickness of thin films of the piezoelectric stack decreases. The film thickness of the resonant bodies is critical and has to be precisely controlled for a desirable resonance frequency. It is difficult and time consuming to trim different areas of a piezoelectric stack to achieve a high level of thickness uniformity for the attainment of a reasonable yield of FBAR and SMR fabrication process for a targeted or specified RF frequency.

5G RF communication systems that are being developed will eventually replace the aforementioned lower performance earlier generation communication systems that operate at RF frequencies between several hundreds of MHz and 1.8 GHz. 5G systems will instead operate at RF frequencies that are much higher, e.g., 3-6 GHz (sub-6 GHz) and possibly all the way up to 100 GHz, or so.

Because of this increase in frequency, the film thickness for FBAR and SMR-based RF filters for 5G applications would have to be reduced in order to increase the resonance frequency, which is one of the challenges current state-of-the-art BAW acoustic resonators face. The reduction in the piezoelectric film thickness means that the distance between top and bottom electrodes of the piezoelectric stack is also reduced, which leads to an increase in electric capacitance. This increase in electrical capacitance leads to a higher feedthrough of RF signal, reducing the signal to noise ratio, which is undesirable. The optimal piezoelectric coupling efficiency of a piezoelectric stack (including top electrode, a bottom electrode, and a piezoelectric layer sandwiched between the top and bottom electrodes) can result from a proper combination of the thickness of the piezoelectric layer, the thickness of the top electrode, the thickness of the bottom electrode, and the alignment and orientation of the piezoelectric crystal(s). The reduction in the piezoelectric film thickness for the purpose of achieving the desirably high RF frequency operation for 5G communication may not allow the attainment of an optimal piezoelectric coupling efficiency, which results in a higher insertion loss and a higher motion impedance. The thickness of the electrodes, either the top electrode, the bottom electrode, or both, may also need to be reduced. Reduction in electrode thickness leads to an increase in electrical resistivity, which leads to another undesirable limitation, namely, higher insertion loss.

Furthermore, the product of frequency and Quality-Factor (or Q) of FBAR and SMR devices are typically constant, which means that an increase in resonance frequency will lead to a decrease in Q. A decrease in Q is undesirable, particularly given that the state of art of FBAR and SMR's Q is approaching the theoretical limit at a frequency 2.45 GHz or below. Therefore, doubling the frequency will lead to a reduction of Q value, which is not desirable for making a RF devices such as an RF filter, an RF resonator, an RF switch, an RF oscillator, etc.

SUMMARY OF THE INVENTION

Generally, provided is a resonator body that can operate in a bulk acoustic mode, preferentially in a lateral resonance mode. The bottom of the resonator body can be mounted or coupled to a mounting substrate or carrier while still allowing the use of the resonator body as an RF filter, an RF resonator, an RF switch, an RF oscillator, etc.

Also provided is a bulk acoustic resonator that includes the resonator body and one or more connecting structures that enable electrical signals to be provided to one or more conductive layers of the resonator body. In one preferred and non-limiting embodiment or example, the one or more connecting structures can be integral with and/or formed from the same layers of materials as the resonator body whereupon the bulk acoustic resonator can be a unitary piece. The bottom of the unitary piece bulk acoustic resonator can be mounted or coupled to a mounting substrate or carrier while still allowing the use of the resonator body as an RF filter, an RF resonator, an RF switch, an RF oscillator, etc.

BRIEF DESCRIPTION OF THE DRAWING(S)

These and other features of the present invention will become more apparent from the following description in which reference is made to the appended drawings wherein:

FIG. 1 is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator (e.g., used herein to describe first and second example unsuspended bulk acoustic resonators) according to the principles of the present invention;

FIG. 2 is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention;

FIG. 3 is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention;

FIG. 4A is an isolated plan view of one preferred and non-limiting embodiment or example form of an interdigitated electrode that can be used as a top conductive layer, an optional bottom conductive layer, or both of an unsuspended bulk acoustic resonator according to the principles of the present invention;

FIG. 4B is an isolated plan view of one preferred and non-limiting embodiment or example form of a comb electrode that can be used as a top conductive layer, an optional bottom conductive layer, or both of an unsuspended bulk acoustic resonator according to the principles of the present invention;

FIG. 4C is an isolated plan view of one preferred and non-limiting embodiment or example form of a sheet electrode that can be used as a top conductive layer, an optional bottom conductive layer, or both of an unsuspended bulk acoustic resonator according to the principles of the present invention;

FIGS. 5A-5B are sections of preferred and non-limiting embodiments or examples taken along lines A-A and B-B in each of FIGS. 1-3;

FIGS. 6A-6B are sections of preferred and non-limiting embodiments or examples taken along lines A-A and B-B in each of FIGS. 1-3;

FIGS. 7A-7B are sections of preferred and non-limiting embodiments or examples taken along lines A-A and B-B in each of FIGS. 1-3;

FIG. 7C is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention with materials of the first and second connecting structures and on both sides of the tether conductors removed as shown in FIGS. 7A-7B;

FIGS. 8A-8B are sections of preferred and non-limiting embodiments or examples taken along lines A-A and B-B in each of FIGS. 1-3;

FIG. 8C is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention with materials of the first and second connecting structures and on both sides of the tether conductors removed as shown in FIGS. 8A-8B;

FIG. 8D is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention with materials of the first and second connecting structures and on both sides of the tether conductors removed as shown in FIGS. 8A-8B;

FIGS. 9A-9B are sections of preferred and non-limiting embodiments or examples taken along lines A-A and B-B in each of FIGS. 1-3;

FIG. 9C is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention with materials of the first and second connecting structures and on both sides of the tether conductors removed as shown in FIGS. 9A-9B;

FIG. 9D is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator according to the principles of the present invention with materials of the first and second connecting structures and on both sides of the tether conductors removed as shown in FIGS. 9A-9B;

FIG. 10 is a plot of frequency vs. dB for a resonator body having a bottom conductive layer in the form of a sheet electrode and a top conductive layer in the form of an comb electrode with a finger pitch of 1.8 μm;

FIG. 11 is an exemplary plot of frequency vs. normalized amplitude showing, in particular, Mode3 and Mode4 resonant frequencies that can be used to explain the frequency responses of first through sixth example unsuspended bulk acoustic resonators described herein;

FIG. 12 is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator (e.g., used herein to describe a third example unsuspended bulk acoustic resonator) according to the principles of the present invention;

FIG. 13 is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator (e.g., used herein to describe fourth and fifth example unsuspended bulk acoustic resonators) according to the principles of the present invention; and

FIG. 14 is a side view of one preferred and non-limiting embodiment or example unsuspended bulk acoustic resonator (e.g., used herein to describe a sixth example unsuspended bulk acoustic resonator) according to the principles of the present invention

DESCRIPTION OF THE INVENTION

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and methods described in the following specification are simply exemplary embodiments, examples, or aspects of the invention. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, in preferred and non-limiting embodiments, examples, or aspects, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. Accordingly, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments, examples, or aspects of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments, examples, or aspects disclosed herein are not to be considered as limiting. Certain preferred and non-limiting embodiments, examples, or aspects of the present invention will be described with reference to the accompanying figures where like reference numbers correspond to like or functionally equivalent elements.

In this application, the use of the singular can include the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. Further, in this application, the use of “a” or “an” means “at least one” unless specifically stated otherwise.

For purposes of the description hereinafter, the terms “end,” “upper,” “lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” “lateral,” “longitudinal,” and derivatives thereof shall relate to the example(s) as oriented in the drawing figures. However, it is to be understood that the example(s) may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific example(s) illustrated in the attached drawings, and described in the following specification, are simply exemplary examples or aspects of the invention. Hence, the specific examples or aspects disclosed herein are not to be construed as limiting.

With reference to FIG. 1, in one preferred and non-limiting embodiment or example, an unsuspended bulk acoustic resonator (UBAR) 2 in accordance with the principles of the present invention, that can be operable in a bulk acoustic mode, can include a resonator body 4 that can include from a top thereof to a bottom thereof a stack of layers comprising a top conductive layer 6, a piezoelectric layer 8, an optional bottom conductive layer 10, and a device layer 12. In the example UBAR 2 shown in FIG. 1, the bottom of device layer 12 can be mounted, e.g., mounted directly, to a mounting substrate or carrier 14.

With reference to FIG. 2 and with continuing reference to FIG. 1, in one preferred and non-limiting embodiment or example, another example UBAR 2 in accordance with the principles of the present invention can be similar to UBAR 2 shown in FIG. 1 with at least the exception that resonator body 4 in FIG. 2 can include an optional substrate 16 between device layer 12 and carrier 14. In an example, the bottom of device layer 12 can be mounted, e.g., mounted directly, to the top of substrate 16 and the bottom of substrate 16 can be mounted, e.g., mounted directly, to carrier 14.

With reference to FIG. 3 and continuing reference to FIGS. 1 and 2, in one preferred and non-limiting embodiment or example, another example UBAR 2 in accordance with the principles of the present invention can be similar to UBAR 2 shown in FIG. 2 with at least the exception that resonator body 4 in FIG. 3 can include an optional second substrate 16-1 between device layer 12 and piezoelectric layer 8 or optional bottom conductive layer 10, if provided, and/or an optional second device layer 12-1 between second substrate 16-1 and piezoelectric layer 8 or optional bottom conductive layer 10, if provided. In one preferred and non-limiting embodiment or example, it is envisioned that resonator body 4 in FIG. 3 can further include one or more additional device layers 12 (not specifically shown) and/or one or more additional substrates 16 (not specifically shown) as deemed suitable and/or desirable. An example resonator body 4 having a number of device layers 12 and substrates 16 can include, in an exemplary order from piezoelectric layer 8 or optional bottom conductive layer 10, if provided, to carrier 14, the following: a first device layer, a first substrate; a second device layer, a second substrate; a third device layer, a third substrate; . . . and so forth. In one preferred and non-limiting embodiment or example, where resonator body 4 can include a plurality of device layers 12 and/or a plurality of substrates 16, each device layer 12 can be made of the same or a different material and each substrate 16 can be made of the same or a different material. In one preferred and non-limiting embodiment or example, the number of device layers 12 and the number of substrates 16 can be different. In an example, in an exemplary order from piezoelectric layer 8 or optional bottom conductive layer 10, if provided, to carrier 14, resonator body 4 can include the following: device layer 12-1, substrate 16-1, and device layer 12 as the bottommost layer of resonator body 4. Examples of materials that can be used to form each device layer 12 and each substrate 16 will be described hereinafter.

In one preferred and non-limiting embodiment or example, as shown in FIGS. 1-3, one or more optional temperature compensation layer 90, 92, and 94 can be provided on the top surface of top conductive layer 6; between piezoelectric layer 8 or optional bottom conductive layer 10, if provided, and device layer 12; and/or between device layer 12 (or 12-1) and substrate 16 (or 16-1), if provided. Each temperature compensation layer can comprise at least one of silicon and oxygen. In an example, each temperature compensation layer can comprise silicon dioxide, or a silicon element, and/or an oxygen element. When provided, the one or more optional temperature compensation layer 90, 92, and 94 can help avoid a change in the resonant frequency of each example resonator body 4 shown in FIGS. 1-3 due to heat generated during use.

In plan view, each resonator body 4 and/or UBAR 2 described herein can have a square or rectangular shape. However, resonator body 4 and/or UBAR 2 having other shapes is envisioned.

With reference to FIGS. 4A-4C and with continuing reference to all previous figures, in one preferred and non-limiting embodiment or example, one or both of conductive layer 6 and optional conductive layer 10 can be in the form of an interdigitated electrode 18 (FIG. 4A) that can include conductive lines or fingers 20, supported by a back 22, interdigitated with conductive lines or fingers 24, supported by a back 26. In one preferred and non-limiting embodiment or example, one or both of conductive layer 6 and optional conductive layer 10 can be in a form of a comb electrode 27 (FIG. 4B) that can include conductive lines or fingers 28 extending from a first back 30. The ends of conductive lines or fingers 28 opposite first back 30 can be connected to an optional second back 32 (shown in phantom in FIG. 4B). In one preferred and non-limiting embodiment or example, one or both of conductive layer 6 and optional conductive layer 10 can be in a form of a conductive sheet electrode 33 (FIG. 4C). Each line or finger 20, 24 and 28 is shown as a straight line. In an example, each line or finger 20, 24 and 28 may be an arched line or finger, a spiral line or finger, or any other suitable and/or desirable shape.

In one preferred and non-limiting embodiment or example, top conductive layer 6 can be in the form of an interdigitated electrode 18, or a comb electrode 27, or a sheet electrode 33. Independent of the form of top conductive layer 6, optional bottom conductive layer 10, if provided, can be in the form of an interdigitated electrode 18, or a comb electrode 27, or a sheet electrode 33. Hereinafter, and for the purpose of description only, in one preferred and non-limiting embodiment or example, top conductive layer 6 will be described as being in the form of a comb electrode 27, that includes the first back 30 and the optional second back 32, and optional bottom conductive layer 10 will be described as being in the form of sheet electrode 33. However, this is not to be construed in a limiting sense since the use is envisioned of any one of interdigitated electrode 18, or comb electrode 27, or sheet electrode 33 for top conductive layer 6, in combination with any one of interdigitated electrode 18, or comb electrode 27, or sheet electrode 33 for optional bottom conductive layer 10.

In one preferred and non-limiting embodiment or example, the resonant frequency of each example resonator body 4 having at least top conductive layer 6 in the form of interdigitated electrode 18 or comb electrode 27, regardless of the form of optional bottom conductive layer 10, if provided, can be tuned or selected in a manner known in the art by appropriate selection of a finger pitch 38 (see e.g., FIGS. 4A-4B), wherein finger pitch 38=finger width+finger gap (between adjacent fingers). In an example, where it is desired that each example resonator body 4 resonate primarily, but not entirely, in lateral mode, versus a thickness mode, the resonant frequency of resonator body 4 can be increased by decreasing the finger pitch 38. In an example, where it is desired that each example resonator body 4 resonate primarily, but not entirely, in the thickness mode, versus lateral mode, the resonant frequency of resonator body 4 can be decreased by increasing the finger pitch 38.

In one preferred and non-limiting embodiment or example, each example resonator body 4 can resonate in a thickness mode, a lateral mode, or a hybrid or a composite mode which is the combination of thickness mode and lateral mode. For thickness mode resonance, the acoustic wave resonates in the direction of piezoelectric layer 8 thickness and the resonant frequency is based on the thickness of the piezoelectric layer 8, and the thickness of the top conductive layer 6 and the optional bottom conductive layer 10, if provided. The combination of piezoelectric layer 8, optional bottom conductive layer 10, if provided, and top conductive layer 6 may be referred to as a piezoelectric stack. The acoustic velocity that determines the resonant frequency of each example resonator body 4 described herein is a composite acoustic velocity of the piezoelectric stack. In an example, the resonant frequency, f, can be calculated by dividing the composite acoustic velocity, V_(a), by twice the piezoelectric stack thickness, τ

For lateral mode resonance, the acoustic wave resonates in a lateral direction (x or y direction) of piezoelectric layer 8 and the resonant frequency can be determined by dividing the composite acoustic velocity of the piezoelectric stack, V_(a), by twice the finger pitch 38, f=V_(a)/2(finger pitch). When the finger pitch is reduced from a large pitch size, δ_(L), to a small pitch size, δ_(S), the percentage of the frequency increase, PFI_(Calculated), can, in an example, be determined by

PFI_(Calculated)=(δ_(L)−δ_(S))/δ_(S).

In an example, when the finger pitch 38 is reduced from 2.2 μm to 1.8 μm, the PFI_(Calculated) for lateral mode is 22.2%. In another example, when the finger pitch 38 is reduced from 1.8 μm to 1.4 μm, the PFI_(Calculated) for a lateral mode is 28.5%.

A composite mode resonance can include a portion of thickness mode resonance and a portion of lateral mode resonance. The portion of the lateral mode resonance, L, in a composite mode resonance can be defined by a ratio of the real or measured percentage of the frequency increase, PFI_(Measured), to a calculated percentage of the frequency increase, PFI_(Calculated), by changing the finger pitch 38 from a large pitch size, δ_(L), to a small pitch size, δ_(S). The lateral mode resonance, L, value can be greater than 100% if there are one or more uncontrolled or unforeseeable variations. In an example, resonator body 4 can resonate in a thickness mode, in a lateral mode, or in a composite mode. In an example of composite mode resonance, the portion of the lateral mode resonance, L, can be ≥20%. In another example of composite mode resonance, the portion of the lateral mode resonance, L, can be ≥30%. In another example of composite mode resonance, the portion of the lateral mode resonance, L, can be ≥40%.

In one preferred and non-limiting embodiment or example, a resonator body 4 having optional bottom conductive layer 10 in the form of sheet electrode 33 and a top conductive layer 6 in the form of comb electrode 27 with a finger pitch 38 of 2.2 μm can resonate in composite mode with the following mode resonant frequencies: Mode1 resonant frequency=1.34 GHz; Mode2 resonant frequency=2.03 GHz; and Mode4 resonant frequency=2.82 GHz.

In an example, for resonator body 4 having optional bottom conductive layer 10 in the form of sheet electrode 33 and a top conductive layer 6 in the form of comb electrode 27 with a finger pitch 38 of 1.8 μm, resonator body 4 can resonate in composite mode with the following mode resonant frequencies: Mode1 resonant frequency=1.49 GHz; Mode2 resonant frequency=2.38 GHz; and Mode4 resonant frequency=3.05 GHz. In this example, the percentage of lateral mode resonance, L, of the composite mode resonance can be: Lmode1=53%; Lmode2=78%; and Lmode4=27%, respectively. See also FIG. 10 which is a plot of frequency vs. dB for this example resonator body 4. In FIG. 10, each peak 82, 84 and 88, represents a response of resonator body 4 at the respective Mode1 resonant frequency=1.49 GHz; the Mode2 resonant frequency=2.38 GHz; and the Mode4 resonant frequency=3.05 GHz.

In an example, the Mode1 resonant frequency may also or alternatively be known as or associated with a surface acoustic wave (SAW); the Mode2 resonant frequency may also or alternatively be known as or associated with an S₀ (or Extensional) mode; and the Mode4 resonant frequency may be also or alternatively be known as or associated with an Ai (or Flexural) mode. Moreover, a Mode3 resonant frequency (discussed hereinafter) may be also or alternatively be known as or associated with a Shear mode. SAW, S₀ mode, Extensional mode, A₁ mode, Shear mode, and Flexural mode are known in the art and will not be described further herein.

In an example, for resonator body 4 having optional bottom conductive layer 10 in the form of sheet electrode 33 and a top conductive layer 6 in the form of comb electrode 27 with a finger pitch 38 of 1.4 μm, resonator body 4 can have the following mode resonant frequencies: Mode1 resonant frequency=1.79 GHz; Mode2 resonant frequency=2.88 GHz; and Mode4 resonant frequency=3.36 GHz. For this example resonator body 4, the percentage of lateral mode resonance, L, of the composite mode resonance can be: Lmode1=70%; Lmode2=74%; and Lmode4=35%.

In an example, the foregoing description of resonator body 4 resonating in a thickness mode, in a lateral mode, or in a composite mode, can also be applicable to each example UBAR 2 shown in FIGS. 1-3 that can include a resonator body 4 in combination with one or more connecting structures 34 and 36, described in more detail hereinafter.

With ongoing reference to FIGS. 1-3, in one preferred and non-limiting embodiment or example, the bottommost layer of each resonator body 4 shown in FIGS. 1-3 can be mounted directly to carrier 14 utilizing any suitable and/or desirable mounting technique, e.g., eutectic mounting, adhesive, etc. Herein, “mounted directly”, “mounting . . . directly”, and similar phrases are to be understood as the bottommost layer of each resonator body 4 shown in FIGS. 1-3 being positioned proximate to carrier 14 and joined to carrier 14 in any suitable and/or desirable manner, such as, in an example, mounting, attaching, etc., and/or by any suitable and/or desirable means, such as, in an example, eutectic bonding, conductive adhesive, non-conductive adhesive, etc. In one preferred and non-limiting embodiment or example, carrier 14 can be a surface of a package, such as an conventional integrated circuit (IC) package. After the bottommost layer of a resonator body 4 is mounted to the surface of said package, resonator body 4, and, more generally, UBAR 2, can, in a manner known in the art, be sealed in said package to protect resonator body 4, and, more generally, UBAR 2, against external environmental conditions. In an example, the use of a package, like a conventional ceramic IC package commercially available from, e.g., NTK Ceramic Co., Ltd. of Japan, for mounting UBAR is envisioned. However, this is not to be construed in a limiting sense since it is envisioned that resonator body 4 and/or UBAR 2 can be mounted in any suitable and/or desirable package now known or hereinafter developed.

In another example, carrier 14 can be the surface of an substrate, such as, for example, a sheet of ceramic, a sheet of conventional printed circuit board material, etc. The description herein of example substrates to which the bottommost layer of each resonator body 4 and/or UBAR 2 shown in FIGS. 1-3 can be mounted is for illustration purposes only and is not to be construed in a limiting sense. Rather, carrier 14 can be made of any suitable and/or desirable material that is not incompatible with the material forming the bottommost layer of each resonator body 4 and/or UBAR 2 shown in FIGS. 1-3 and which enables the use of resonator body 4 and/or UBAR 2 in a manner known in the art. Carrier 14 can have any form deemed suitable and/or desirable by one skilled in the art. Accordingly, any description herein of mounting substrate or carrier 14 is not to be construed in a limiting sense.

With ongoing reference to FIGS. 1-3, in one preferred and non-limiting embodiment or example, each UBAR 2 can include one or more optional connecting structures 34 and/or 36 that facilitate the application of electrical signals to top conductive layer 6 and optional bottom conductive layer 10, if provided, of resonator body 4. In one preferred and non-limiting embodiment or example, however, the one or more optional connecting structures 34 and/or 36 may be excluded (i.e., not provided) where electrical signals can be applied directly to top conductive layer 6 and optional bottom conductive layer 10, if provided, of resonator body 4. Accordingly, in an example, UBAR 2 can comprise resonator body 4 without connecting structures 34 and 36. In another example, UBAR 2 can comprise resonator body 4 and a single connecting structure 34 or 36. For the purpose of description only, in one preferred and non-limiting embodiment or example, UBAR 2 comprising resonator body 4 and connecting structures 34 and 36 will be described.

Each connecting structure 34 and 36 can have any suitable and/or desirable form, can be formed in any suitable and/or desirable manner, and can be made of any suitable and/or desirable material(s) that can facilitate the provision of separate electrical signals to top conductive layer 6 and optional bottom conductive layer 10, if provided. In an example, where top conductive layer 6 is in the form of comb electrode 27 with only one back 30 or 32, and optional bottom conductive layer 10 is in the form of comb electrode 27 with only one back 30 or 32, or sheet electrode 33, electrical signals can be provided to each of top conductive layer 6 and optional bottom conductive layer 10 via a single connecting structure 34 or 36 that can be configured to provide separate electrical signals to top conductive layer 6 and optional bottom conductive layer 10.

In another example, where at least one of top conductive layer 6 or optional bottom conductive layer 10 has the form of interdigitated electrode 18 or comb electrode 27 having two backs 30 and 32, separate connecting structures 34 and 36 can be provided to separately provide one or more electrical signals to backs 24 and 26 of interdigitated electrode 18 and/or to backs 30 and 32 of comb electrode 27. The forms of top conductive layer 6 and optional bottom conductive layer 10 and manner in which electrical signals are provided to top conductive layer 6 and optional bottom conductive layer 10, if provided, is not be construed in a limiting sense.

In one preferred and non-limiting embodiment or example, while not wishing to be bound by any particular description, example, or theory, examples of first and second connecting structures 34 and 36 that can be used with the example UBARs 2 shown in FIGS. 1-3 will be described next.

In one preferred and non-limiting embodiment or example, for the purpose of description only, each connecting structure 34 and 36 will be described as having extensions of the various layers and/or substrates forming the various examples resonator bodies 4 shown in FIGS. 1-3. However, this is not to be construed in a limiting sense since it is envisioned that each connecting structure 34 and 36 can have any suitable and/or desirable form and/or structure that enable the provision of one or more separate electrical signals to top conductive layer 6 and optional bottom conductive layer 10, if provided.

In one preferred and non-limiting embodiment or example, with reference to FIGS. 5A-5B, which can represent views taken along lines A-A and B-B in any one or all of FIGS. 1-3, FIG. 5A shows top conductive layer 6 in the form of comb electrode 27, including back 30 and optional back 32, on top of piezoelectric layer 8. In an example, top conductive layer 6 can alternatively be in the form of interdigitated electrode 18. In one preferred and non-limiting embodiment or example, FIG. 5B shows optional bottom conductive layer 10 in the form of sheet electrode 33 below piezoelectric layer 8 (shown in phantom lines in FIG. 5B). In an example, optional bottom conductive layer 10 can alternatively be in the form of interdigitated electrode 18 or comb electrode 27. For the purpose of the following examples only, top conductive layer 6 and optional bottom conductive layer 10 will be described as being in the form of comb electrode 18, including back 30 and optional back 32, and sheet electrode 33, respectively. However, this is not to be construed in a limiting sense.

In one preferred and non-limiting embodiment or example, connecting structures 34 and 36 can include bottom metal layers 40 and 44 (FIG. 5B) in contact with sheet electrode 33 forming optional bottom conductive layer 10 of resonator body 4. Each bottom layer 40 and 44 can be in the form of a sheet that is covered by piezoelectric layer 8. In an example, each bottom layer 40 and 44 can be an extension of and can be formed at the same time as sheet electrode 33. In another example, each bottom layer 40 and 44 can be formed separately from sheet electrode 33 and can be made from the same or different material as sheet electrode 33. In an example, connecting structures 34 and 36 can also include top metal layers 42 and 46 on top of piezoelectric layer 8 and in contact with back 30 and back 32, respectively, of comb electrode 27 forming top conductive layer 6 of resonator body 4.

In an example, bottom metal layers 40 and 44 can be connected to contact pads 48 on top surfaces of first and second connecting structures 34 and 36 via conductive vias 50 formed in piezoelectric layer 8 that extend between said contact pads 48 and bottom metal layers 40 and 44. In an example, each top metal layer 42 and 46 can have the shape of a sheet that spaced from the corresponding contact pads 48 by a gap (not numbered). Each top metal layer 42 and 46 can also include a contact pad 58. Each contact pad 48 can be connected, as needed/required, to a suitable signal source (not shown) that can be used to electrical drive/bias optional bottom conductive layer 10 in any suitable and/or desirable manner. Similarly, each contact pad 58 can be connected, as needed/required, to a suitable signal source (not shown) that can be used to drive/bias top conductive layer 6 in any suitable and/or desirable manner.

As shown by reference numbers 18 and 27 in FIGS. 5A-5B, top conductive layer 6 can alternatively be in the form of interdigitated electrode 18 and optional bottom conductive layer 10 can alternatively be in the form of comb electrode 27 or interdigitated electrode 18.

With reference to FIGS. 6A-6B, which can represent views taken along lines A-A and B-B in any one or all of FIGS. 1-3, in one preferred and non-limiting embodiment or example, the examples shown in FIGS. 6A-6B are similar to the examples shown FIGS. 5A-5B with at least the following exception. Bottom metal layers 40 and 44 can each be in the form a pair of spaced conductors 52 (versus the conductive sheets shown in FIGS. 5A-5B) that are connected to optional bottom conductive layer 10 in the form of sheet electrode 33 by a lateral conductor 54 and a tether conductor 56. Top metal layers 42 and 46 can each be in the form a conductor 60. Each conductor 60 can be connected to back 30 or back 32 of comb electrode 27 forming top conductive layer 6 by a tether conductor 62. Tether conductor 62 can be vertically aligned with tether conductor 56 and spaced therefrom by piezoelectric layer 8. In an example, as shown in FIGS. 6A-6B, the width of tether conductor 62 can be less than the width of conductor 60 and the width of tether conductor 56 can be about the same as the width of tether conductor 62.

With reference to FIGS. 7A-7B, which can represent views taken along lines A-A and B-B in any one or all of FIGS. 1-3, in one preferred and non-limiting embodiment or example, the examples shown in FIGS. 7A-7B are similar to the examples shown in FIGS. 6A-6B with at least the following exception. Some or all of the materials of each connecting structure 34 and 36 on both sides of the tether conductor(s) 62 and 56, if provided, of said connecting structure can be removed, thereby forming slots that can extend some or all of the distance from the top to the bottom of UBAR 2 on both sides of said tether conductor(s) between the remaining part of said connecting structure and resonator body 4. The removal of some or all of the materials of each connecting structure 34 and 36 on both sides of the tether conductor(s) of said connecting structure can, in an example, define a tether structure 76 that can include tether conductor(s) 62 and 56, if provided, and the portion of the piezoelectric layer 8 in vertical alignment with tether conductor 62.

With reference to FIG. 7C and with continuing reference to FIGS. 7A-7B, in one preferred and non-limiting embodiment or example, the removal of some or all of the materials forming each connecting structure 34 and 36 on both sides of the tether conductor(s) 62 and 56, if provided, of said connecting structure can be used with any example UBAR 2 shown in FIGS. 1-3. For example, FIG. 7C shows a side view of the example UBAR 2 shown in FIG. 1 with the materials of first and second connecting structures 34 and 36 on both sides of the tether conductor 62 and 56, if provided, of each said connecting structure removed, as shown in FIGS. 7A-7B. As can be understood from FIGS. 7A-7C, the materials removed on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure can include portions of top conductive layer 6, piezoelectric layer 8, optional bottom conductive layer 10, if provided, and device layer 12, whereupon, in the views shown in FIGS. 7A-7B, no material is visible in the slots formed by the removal of these materials of each connecting structure 34 and 36 on both sides of tether conductor(s) 62 and 56, if provided, of said connecting structure. In the example shown in FIGS. 7A-7C, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when bottom conductive layer 10 is present), and a portion of device layer 12 in vertical alignment with tether conductor 62.

In another example, where a UBAR 2 includes substrate 16 (FIG. 2), shown in phantom in FIG. 7C, and, optionally, one or more additional device layers 12-1 and/or substrates 16-1 (FIG. 3), the material forming substrate 16 and, if provided, each additional device layer 12-1 and/or substrate 16-1 on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure 34 and 36 can also be removed, whereupon, in the views shown in FIGS. 7A-7B, no material would be visible in the slots formed by the removal of these materials of each connecting structure 34 and 36 on both sides of the tether conductor(s) 62 and 56, if provided, of said connecting structure.

In an example, where the views shown in FIGS. 7A-7B are of the example UBAR 2 shown in FIG. 2, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), a portion of device layer 12 in vertical alignment with tether conductor 62, and a portion of substrate 16 in vertical alignment with the portion of device layer 12. In another example, where the views shown in FIGS. 7A-7B are of the example UBAR 2 shown in FIG. 3, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), portions of device layers 12 and 12-1 in vertical alignment with tether conductor 62, and portions of substrates 16 and 16-1 in vertical alignment with tether conductor 62.

With reference to FIGS. 8A-8B, which can represent views taken along lines A-A and B-B in any one or all of FIGS. 1-3, in one preferred and non-limiting embodiment or example, the examples shown in FIGS. 8A-8B are similar to examples shown in FIGS. 7A-7B with at least the following exception. Namely, the material forming all or part of at least one device layer 12 or 12-1 of each connecting structure 34 and 36 is retained on both sides of the tether conductor(s) 62 and 56, if provided, of said connecting structure, whereupon said material of said at least one device layer 12 or 12-1 is visible in the slots on both sides of the tether conductor(s) 62 and 56, if provided, of said connecting structure. In an example, where the views shown in FIGS. 8A-8C are of the example UBAR 2 shown in FIG. 1, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, and optional tether conductor 56 (when optional bottom conductive layer 10 is present). In this example, device layer 12 is retained and would be visible in the slots shown in FIGS. 8A-8B.

In another example, where the views shown in FIGS. 8A-8B are of the example UBAR 2 shown in FIG. 2, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and a portion of device layer 12 in vertical alignment with tether conductor 62. In this example, device layer 12 is retained and would be visible in the slots shown in FIGS. 8A-8B and substrate 16 (shown in phantom in FIG. 8C) below device layer 12 would also be retained, but would not be visible in the slots shown in FIGS. 8A-8B.

In another example, where the views shown in FIGS. 8A-8B are of the example UBAR 2 shown in FIG. 3, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and a portion of device layer 12 in vertical alignment with tether conductor 62. In an example, where device layer 12 is retained and is visible in the slots shown in FIGS. 8A-8B, substrate 16 below device layer 12 is also retained, but would not be visible in the slots shown in FIGS. 8A-8B, and each tether structure 76 would also include a portion of device layer 12-1 and a portion of substrate 16-1 in vertical alignment with tether conductor 62. In another example, where device layer 12-1 is retained and is visible in the slots shown in FIGS. 8A-8B, substrates 16 and 16-1 and device layer 12 would also be retained, but would not be visible in the slots shown in FIGS. 8A-8B.

In another example shown in FIG. 8D, for the example UBAR 2 shown in FIG. 1 or 2, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and a portion of the body of device layer 12 in vertical alignment with tether conductor 62 exposed by the partial removal of device layer 12 on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure 34 and 36. Where the example shown in FIG. 8D is UBAR 2 shown in FIG. 2, substrate 16 (shown in phantom in FIG. 8D) is retained below device layer 12 and would not be visible in the views shown in FIGS. 8A-8B.

In another example, for the example UBAR 2 shown in FIG. 3, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and a portion of the body of device layer 12 or device layer 12-1 in vertical alignment with tether conductor 62 exposed by the partial removal of said device layer 12 or 12-1 (similar to the partial removal of device layer 12 shown in FIG. 8D) on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure 34 and 36. In an example, where the portion of the body of device layer 12 of UBAR 2 shown in FIG. 3 is removed (similar to the partial removal of device layer 12 shown in FIG. 8D), whereupon the portion of the interior of the material forming device layer 12 of UBAR 2 shown in FIG. 3 is visible in the slots shown in FIGS. 8A-8B, each tether structure 76 can also include portions of device layer 12-1 and substrate 16-1 in vertical alignment with tether conductor 62. In this example, substrate 16 is retained, i.e., no portion of substrate 16 is removed, and would not be visible in the views shown in FIGS. 8A-8B.

In another example, where the portion of the body of device layer 12-1 of UBAR 2 shown in FIG. 3 is removed (similar to the partial removal of device layer 12 shown in FIG. 8D), whereupon the portion of the interior of the material forming device layer 12-1 is visible in the slots shown in FIGS. 8A-8B, each tether structure 76 can also include a portion of the body of device layer 12-1 in vertical alignment with tether conductor 62. In this example, substrates 16 and 16-1 and device layer 12 are retained, i.e., no portions of substrates 16 and 16-1 and device layer 12 are removed, and would not be visible in the views shown in FIGS. 8A-8B.

With reference to FIGS. 9A-9B, which can represent views taken along lines A-A and B-B in any one or all of FIGS. 1-3, for the UBAR 2 shown in FIG. 2, in one preferred and non-limiting embodiment or example, the examples shown in FIGS. 9A-9B are similar to the examples shown in FIGS. 8A-8B with at least the following exception. Each tether structure 76 can include a portion of the material forming device layer 12, whereupon in the views shown in FIGS. 9A-9C, portions of substrate 16 can be visible in the slots formed on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure 34 and 36. In this example, substrate 16 is retained and each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and a portion of device layer 12 in vertical alignment with tether conductor 62.

With continuing reference to FIGS. 9A-9B, for the UBAR 2 shown in FIG. 3, in one preferred and non-limiting embodiment or example, where device layer 12 and substrates 16 and 16-1 are retained, in the views shown in shown in FIGS. 9A-9B, substrate 16-1 can be visible in the slots formed on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure 34 and 36. In this example, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and a portion of device layer 12-1 in vertical alignment with tether conductor 62.

In another example, for the UBAR 2 shown in FIG. 3, where substrate 16 is retained, whereupon, in the views shown in FIGS. 9A-9B, substrate 16 can be visible in the slots formed on both sides of the tether conductor(s) 62 and 56, if provided, of each connecting structure 34 and 36, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), a portion of device layer 12-1 in vertical alignment with tether conductor 62, a portion of substrate 16-1 in vertical alignment with tether conductor 62, and a portion of device layer 12 in vertical alignment with tether conductor 62.

In another example shown in FIG. 9D, for the example UBAR 2 shown in FIG. 2, at the interface of substrate 16 and device layer 12, a portion of the material forming the body of substrate 16 can be removed laterally beneath resonator body 4 and connecting structures 34 and 36, whereupon, as shown in FIG. 9D, bottom portions 64 and 70 of connecting structures 34 and 36 are exposed, bottom portions 66 and 68 of resonator body 4 are exposed, and surfaces 72 and 74 of the body of substrate 16 are exposed. In this example, a portion of the material forming the body of substrate 16 removed can extend into the plane of FIG. 9D to the portion of the material of substrate 16 vertically aligned with each tether structure 76. In this example, each tether structure 76 can include, from top to bottom, tether conductor 62, a portion of piezoelectric layer 8 in vertical alignment with tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), a portion of device layer 12 in vertical alignment with tether conductor 62, and a portion of substrate 16 in vertical alignment with tether conductor 62 proximate the portion of device layer 12. In this example, surfaces 72 and 74 can be visible in the slots shown in FIGS. 9A-9B.

In another, alternative example, for the example UBAR 2 shown in FIG. 3, a portion of the material forming substrate 16-1 or 16 can be removed laterally beneath resonator body 4 and connecting structures 34 and 36, similar to the removal of the material forming substrate 16 in FIG. 9D, whereupon surfaces (like surfaces 72 and 74) of the material forming substrate 16-1 or 16 are exposed and can be visible in the slots shown in FIGS. 9A-9B.

In an example, where the surfaces (like surfaces 72 and 74) of the material forming substrate 16-1 of the example UBAR 2 of FIG. 3 are exposed and can be visible in the slots shown in FIGS. 9A-9B, each tether structure 76 can also include a portion of device layer 12-1 in vertical alignment with tether conductor 62 and a portion of material forming substrate 16-1 in vertical alignment with tether conductor 62 proximate device layer 12-1. In this example, only a portion of the body of substrate 16-1 is removed to form each slot, and device layer 12 and substrate 16 are retained, i.e., no portions of device layer 12 and substrate 16 are removed, and are not visible in the views shown in FIGS. 9A-9B.

In another example, where the surfaces (like surfaces 72 and 74) of the material forming substrate 16 of the example UBAR 2 of FIG. 3 are exposed and can be visible in the slots shown in FIGS. 9A-9B, each tether structure 76 can also a portion of device layer 12-1 in vertical alignment with tether conductor 62, a portion substrate 16-1 in vertical alignment with tether conductor 62, a portion device layer 12 in vertical alignment with tether conductor 62, and a portion of the material forming substrate 16 in vertical alignment with tether conductor 62 proximate device layer 12. In this example, only a portion of the body of substrate 16 is removed to form each slot.

In one preferred and non-limiting embodiment or example, in any of the examples discussed above where bottom conductive layer 10 is not present, bottom metal layers 40 and 44 of connecting structures 34 and 36 need not be present.

In one preferred and non-limiting embodiment or example, each tether structure 76 described above can include at least tether conductor 62, optional tether conductor 56 (when optional bottom conductive layer 10 is present), and only the portion of piezoelectric layer 8 in vertical alignment with tether conductor 62. In another preferred and non-limiting embodiment or example, each tether structure 76 can also include only the portions of one or more of the following in vertical alignment with tether conductor 62: device layer 12, substrate 16, device layer 16-1, and/or substrate 16-1. However, this is not to be construed in a limiting sense.

In one preferred and non-limiting embodiment or example, for each example resonator body 4 shown in FIGS. 1-3, the widths of at least top conductive layer 6, optional bottom conductive layer 10, if provided, and the portion of piezoelectric layer 8 below top conductive layer 6 can all be the same. Also or alternatively, in an example, the widths and/or dimensions of device layer 12, substrate 16, and, if provided, device layer 12-1 and/or substrate 16-1, can all be the same as the widths and/or dimensions of top conductive layer 6, optional bottom conductive layer 10, if provided, and piezoelectric layer 8.

In one preferred and non-limiting embodiment or example, any one or more of the surfaces of any example resonator body 4 shown in FIGS. 1-3 and/or one or all of the surfaces of anyone or more connecting structures 34 and/or 36, if provided, can be etched as deemed suitable and/or desirable to optimize the quality factor and/or insertion loss of any example UBAR 2 shown in FIGS. 1-3. For example, top and bottom surfaces of any example resonator body 4 shown in FIGS. 1-3 can be etched. Also or alternatively, one or more side surfaces of any example resonator body 4 shown in FIGS. 1-3 can be etched, whereupon each of said side surfaces can be vertically planar.

In one preferred and non-limiting embodiment or example, where top conductive layer 6, optional bottom conductive layer 10, if provided, or both are in the form interdigitated electrode 18, one back 22 or 26 of said interdigitated electrode 18 can be connect to and driven by a suitable signal source while the other back 22 or 26 can be unconnected to a signal source. In another preferred and non-limiting embodiment or example, where top conductive layer 6, optional bottom conductive layer 10, if provided, or both are in the form interdigitated electrode 18, back 22 of said interdigitated electrode 18 can be connect to and driven by one signal source and back 26 of said interdigitated electrode 18 can be connect to and driven by a second signal source. In an example, the second signal source can be the same or different than the first signal source.

In one preferred and non-limiting embodiment or example, each instance of device layer 12 (or 12-1) can have an acoustic impedance ≥60×10⁶ Pa-s/m³. In another example, each instance of device layer 12 (or 12-1) can have an acoustic impedance ≥90×10⁶ Pa-s/m³. In another example, each instance of device layer 12 (or 12-1) can have an acoustic impedance ≥500×10⁶ Pa-s/m³. In one preferred and non-limiting embodiment or example, each substrate layer 16 can have an acoustic impedance ≤100×10⁶ Pa-s/m³. In another example, each substrate layer 16 can have an acoustic impedance ≤60×10⁶ Pa-s/m³.

In one preferred and non-limiting embodiment or example, the reflectance (R) of an acoustic wave at the interface of device layer 12 and piezoelectric layer 8 or, if provided, optional bottom conductive layer 10, can be greater than 50%. In another example, the reflectance (R) of an acoustic wave at the interface of device layer 12 and piezoelectric layer 8 or, if provided, optional bottom conductive layer 10, can be greater than 70%. In another example, the reflectance (R) of an acoustic wave at the interface of device layer 12 and piezoelectric layer 8 or, if provided, optional bottom conductive layer 10, can be greater than 90%.

In one preferred and non-limiting embodiment or example, the reflectance (R) of an acoustic wave at the interface of a device layer 12 or 12-1 and piezoelectric layer 8 or, if provided, optional bottom conductive layer 10, can be greater than 70%. In an example, the reflectance R at the interface of any two layers 6 and 8; 8 and 10; 8 or 10 and 12 or 12-1; or 12 or 12-1 and 16 or 16-1, or at the interface of a device layer 12 or 12-1 and a substrate 16 or 16-1 can be determined according to the following equation:

R=|(Zb−Za)/(Za+Zb)|

wherein Za=the acoustic impedance of a first layer, e.g., piezoelectric layer 8 or, if provided, optional bottom conductive layer 10, that sits atop of a second layer; and

Zb=the acoustic impedance of the second layer, e.g., device layer 12.

Other examples of first and second layers can include instances of device layer 12 or 12-1 atop of substrate 16 or 16-1.

In one preferred and non-limiting embodiment or example, the overall reflectance (R) of any example resonator body 4 shown in FIGS. 1-3 can be >90%.

In one preferred and non-limiting embodiment or example, device layer 12 can be a layer of diamond or SiC formed in a manner known in the art. In an example, substrate 16 can be formed from silicon.

In one preferred and non-limiting embodiment or example, device layer 12 formed of diamond can be grown by chemical vapor deposition (CVD) of diamond on a substrate 16 or 16-1 or a sacrificial substrate (not shown). In one preferred and non-limiting embodiment or example, optional bottom conductive layer 10, piezoelectric layer 8, and top conductive layer 6 can be deposited on device layer 12 and, as required, patterned (e.g., comb electrode 27 or interdigitated electrode 18) utilizing conventional semiconductor processing techniques which will not be described further herein.

Herein, each temperature compensation layer 90, 92, and 94 can comprise at least one of silicon and oxygen. For example, each temperature compensation layer can comprise silicon dioxide, or a silicon element, and/or an oxygen element.

In one preferred and non-limiting embodiment or example, each UBAR 2 shown in FIGS. 1-3 can have an unloaded quality factor ≥100. In another example, each UBAR 2 shown in FIGS. 1-3 can have an unloaded quality factor ≥50. In one preferred and non-limiting embodiment or example, the thickness of piezoelectric layer 8, each device layer 12, and, if provided, each substrate 16 of each example resonator body 4 shown in FIGS. 1-3, can be selected in any suitable and/or desirable manner to optimize the performance of resonator body 4. Similarly, in an example, the dimensions of each example resonator body 4 shown in FIGS. 1-3, can be selected for target performance such as, without limitation, insertion lost, power handling capability, and thermal dissipation. In one preferred and non-limiting embodiment or example, when diamond is used as the material for a device layer 12, the surface of said diamond layer at the interface with bottom layer 12 can be optically finished and/or physically dense. In an example, the diamond material forming device layer 12 can be undoped or doped, e.g., P-type or N-type. The diamond material can be polycrystalline, nanocrystalline, or ultrananocrystalline. In an example, when silicon is used as the material for each instance of substrate 16, said silicon can be undoped or doped, e.g., P-type or N-type, and monocrystalline or polycrystalline. The diamond material forming the device layer can have a Raman half-height-peak-width of ≤20 cm⁻¹.

In one preferred and non-limiting embodiment or example, piezoelectric layer 8 can be formed of ZnO, AlN, InN, alkali metal or alkali earth metal niobate, alkali metal or alkali earth metal titanate, alkali metal or alkali earth metal tantalite, GaN, AlGaN, lead zirconate titanate (PZT), polymer or a doped form of any of the foregoing materials.

In one preferred and non-limiting embodiment or example, device layer 12 can be formed of any suitable and/or desirable high acoustic impedance material. In an example, a material having an acoustic impedance between 10⁶ Pa-s/m³ and 630×10⁶ Pa-s/m³ or greater can be considered a high acoustic impedance material. Some non-limiting examples of typical high acoustic impedance materials that can be used, for example, to form any device layer 12 described herein, may include: diamond (˜630×10⁶ Pa-s/m³); W (˜99.7×10⁶ Pa-s/m³); SiC; a condensed phase material such as a metal, e.g., Al, Pt, Pd, Mo, Cr, Ir, Ti, Ta; an element from Group 3A or 4A of the periodic table; a transition element from Group 1B, 2B, 3B, 4B, 5B, 6B, 7B, or 8B of the periodic table; ceramic; glass, and polymer. This list of non-limiting example high acoustic impedance materials is not to be construed in a limiting sense.

In one preferred and non-limiting embodiment or example, substrate 16 can be formed of any suitable and/or desirable low acoustic impedance material. In an example, a material having an acoustic impedance between 10⁶ Pa-s/m³ and 30×10⁶ Pa-s/m³ can be considered a low acoustic impedance material. Some non-limiting examples of typical low acoustic impedance materials that can be used, for example, to form any substrate 16 described herein, may include at least one of: ceramic; glass, crystals, minerals, and a metal having an acoustic impedance between 10⁶ Pa-s/m³ and 30×10⁶ Pa-s/m³; ivory (1.4×10⁶ Pa-s/m³); alumina/sapphire (25.5×10⁶ Pa-s/m³); alkali metal K (1.4×10⁶ Pa-s/m³); SiO₂, and silicon (19.7×10⁶ Pa-s/m³). This list of non-limiting example low acoustic impedance materials is not to be construed in a limiting sense.

In one preferred and non-limiting embodiment or example, depending on choice of materials forming each example resonator body 4, one or more materials typically considered to be high acoustic impedance materials can function as a low acoustic impedance material of resonator body 4. For example, where diamond or SiC is used as the material for device layer 12, W can be used as the material for substrate 16. Hence, achieving a desired reflectance R (discussed above) at an interface of two layers or substrates of resonator body 4 can determine which material can be used as a high acoustic impedance material and which material can be used as a low acoustic impedance material.

In one preferred and non-limiting embodiment or example, a bulk acoustic resonator, in accordance with the principles of the present invention, can include a resonator body 4. The resonator body 4 can include a piezoelectric layer 8; a device layer 12; and a top conductive layer 6 on the piezoelectric layer 8 opposite the device layer 12. Substantially all of a surface of the device layer 12 opposite the piezoelectric layer is for mounting the resonator body 4 to a carrier 14 that is separate from the resonator body 4. In the example, it is desirable but not essential that all of the surface of the device layer opposite the piezoelectric layer can be for mounting the entirety of the resonator body to the carrier. In the example, it is desirable but not essential that the bulk acoustic resonator can include a connecting structure 34 or 36 for conducting a signal to the top conductive layer. In an example, the device layer can comprise diamond or SiC. In an example, the top conductive layer 6 can include a plurality of spaced conductive lines or fingers. In an example, the resonator body 4 can further comprise an optional bottom conductive layer 10 between the piezoelectric layer 8 and the device layer 12.

In one preferred and non-limiting embodiment or example, the resonator body 4 can further include a substrate 16 attached to the device layer 12 opposite the piezoelectric layer 8. In an example, the surface of the device layer 12 can be mounted in its entirety to the substrate 16. In an example, the surface of the substrate 16 facing the carrier 14 can be for mounting in its entirety directly to the carrier 14.

In one preferred and non-limiting embodiment or example, the surface of the device layer 12 facing the carrier 14 can be mounted in its entirety directly to the substrate 16. In an example, the surface of the device layer 12 facing the carrier 14 is for mounting in its entirety directly to the carrier 14.

In one preferred and non-limiting embodiment or example, the resonator body 4 can further include a second device layer 12-1 between the substrate 16 and the piezoelectric layer 8; or a second substrate 16-1 between the substrate 16 and the piezoelectric layer 8; or both.

In one preferred and non-limiting embodiment or example, as used herein, “mounting in its entirety” can mean mounting one layer or substrate directly or indirectly to another layer or substrate. In an example, as used herein, “mounting in its entirety” can, also or alternatively, mean without an intentionally introduced space or gap between one layer or substrate and another layer or substrate. In another example, as used herein, “mounting in its entirety” can, also or alternatively, include naturally occurring spaces that can naturally (but not intentionally) form between one layer or substrate and another layer or substrate.

Having thus described some non-limiting embodiment or example UBARs, first through sixth examples of UBARs will be now be described.

First Example UBAR: A Device-Layer-Enabled Mode3 and or Mode4 Resonance with the Presence of a Temperature-Compensation Layer

Referring back to FIG. 1, in some non-limiting embodiments or examples, a first example UBAR 2 (shown in FIG. 1) can include, from a top thereof to carrier 14, top conductive layer 6 comprising spaced conductive lines or fingers 20 or 28 (shown in FIGS. 4A-4B), piezoelectric layer 8 formed of LiNbO₃, temperature compensation layer 92 formed of SiO₂, and device layer 12 formed of diamond or SiC. In an example, finger pitch 38 (shown in FIGS. 4A-4B) is 0.6 μm and the thickness of piezoelectric layer 8 is 0.6 μm.

Throughout this disclosure, the value of a variable “k” may be based on one or more dimensions of a pattern or feature defined by top conductive layer 6 or based on a thickness of piezoelectric layer 8. In some non-limiting embodiments or examples, the value of λ may be equal to 2 times the finger pitch 38 or may be equal to 2 times the thickness of piezoelectric layer 8 (in this example 1.2 μm). However, this is not to be construed in a limiting sense since the value of λ may be based on any other suitable and/or desirable dimension of one or more other patterns or features and/or thickness of one or more layers of each example UBAR described herein. In this example, the cut angle of piezoelectric layer 8 was 0° (or 180°), sometimes called a Y-Cut or an YX-Cut. In some non-limiting embodiments or examples, the use of a cut angle of piezoelectric layer 8 of 0° (or 180°)±20° is envisioned. Herein, unless otherwise indicated, a cut angle of piezoelectric layer 8 is with reference to a cut angle rotated about the X axis.

In some non-limiting embodiments or examples, for the purpose of modeling the first example UBAR 2, frequency responses (frequency vs. amplitude) were determined for frequency sweeps (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to this first example UBAR 2 for a number or plurality of different exemplary values of thickness of the temperature compensation layer 92 formed of SiO₂. In an example modeling, the thickness of the temperature compensation layer 92 formed of SiO₂ was varied between ( 9/16)λ and ( 1/64)λ and the frequency of the exemplary electrical stimulus applied to the first example, UBAR 2 for each value of thickness was varied between at least 1 GHz and 6.2 GHz. In an example, a first plot, graph, or relationship of frequency vs. amplitude was determined for a frequency sweep between at least 1 GHz and 6.2 GHz for a thickness of the temperature compensation layer 92 of ( 9/16)λ, for example. In an example, another plot, graph, or relationship of frequency vs. amplitude was determined for a frequency sweep between at least 1 GHz and 6.2 GHz for a thickness of the temperature compensation layer 92 of ( 3/64)λ, for example. Additional plots, graphs, or relationships of frequency vs. amplitude were determined for frequency sweeps of other thicknesses of the temperature compensation layer 92.

For each plot, graph, or relationship of frequency vs. amplitude, at least the Mode4 resonant frequency 88 (FIGS. 10 and 11) was observed. In this first example UBAR, however, surprisingly, the Mode4 resonant frequency 88 was observed (FIG. 11) at about 5.2 GHz, versus 3.05 GHz for the Mode4 resonant frequency 88 shown in FIG. 10 and a Mode3 resonant frequency 86 (FIG. 11) was observed at about 3.13 GHz.

In FIG. 11, the Mode1 and Mode2 resonant frequencies 82 and 84 (shown for example in FIG. 10) are omitted to the left of the Mode3 resonant frequency 86 for simplicity. However, it is to be understood that for frequency sweep between at least 1 GHz and 6.2 GHz Mode1 and Mode2 resonant frequencies 82 and 84 (shown for example in FIG. 10) may be present in addition to the Mode3 and Mode4 resonant frequencies 86 and 88.

In some non-limiting embodiments or examples, as shown for example in FIG. 11, each plot, graph, or relationship of frequency vs. amplitude includes a positive peak value of f_(s1) and a negative peak value of f_(p1) for the Mode3 resonant frequency 86, and includes a positive peak value of f_(s2) and a negative peak value of f_(p2) for the Mode4 resonant frequency 88.

For the purpose of description only, as used herein, a “resonant frequency” observed “about” a particular frequency can be, for the Mode3 resonant frequency 86, any representative frequency between the positive peak value f_(s1) and the negative peak value of f_(p1), and, for the Mode4 resonant frequency 88, the positive peak value f_(s2) and the negative peak value of f_(p2). Accordingly, any resonant frequency described herein as being “about” a particular frequency is not to be construed in a limiting sense.

In some non-limiting embodiments or examples, for a thickness ( 1/16)λ of the temperature compensation layer 92 formed of SiO₂, the Mode3 coupling efficiency (M3CE) and the Mode4 coupling efficiency (M4CE) for the Mode3 and Mode4 resonant frequencies 86 and 88 can be determined the following equations EQ1 and EQ2, respectively:

Mode3 Coupling Efficiency(M3CE)=(π²/4)((f _(p1) −f _(s1))/f _(p1))  EQ1:

Mode4 Coupling Efficiency(M4CE)=(π²/4)((f _(p2) −f _(s2))/f _(p2))  EQ2:

wherein:

-   -   for exemplary values of f_(p1) and f_(s1) equal to 3.738 GHz and         3.13 GHz, respectively, M3CE=40.093%; and     -   for exemplary values of f_(p2) and f_(s2) equal to 5.442 GHz and         5.172 GHz, respectively, M4CE=12.229%.

However, the foregoing value of M3CE in this example is not to be construed in a limiting sense since a value of M3CE ≥8%, ≥11%, ≥14%, ≥17%, or ≥20% may be satisfactory, suitable, and/or desirable. Also or alternatively, the foregoing value of M4CE in this example is not to be construed in a limiting sense since a value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be satisfactory, suitable, and/or desirable.

In some non-limiting embodiments or examples, when a specific value of M3CE, for example, ≥8%, ≥11%, ≥14%, ≥17%, or ≥20%, is desired, the cut angle of piezoelectric layer 8 may extend beyond the above cut angle of 0° (or 180°)±20°, e.g., a cut angle of 0° (or 180°)≥±20°, ≥±30°, ≥±40°, ≥±50°, etc. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M3CE.

In some non-limiting embodiments or examples, when a certain level of M4CE, for example, ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, is desired, the cut angle of piezoelectric layer 8 may extend beyond a cut angle of 130°±30° (sometimes called a Y-Cut130±30 or a YX-cut130±30), e.g., a cut angle of 130°≥±30°, ≥±40°, ≥±50°, etc. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M4CE.

In some non-limiting embodiments or examples, using equations EQ1 and EQ2 and plots, graphs, or relationships of frequency vs. amplitude determined in the manner described above for a number of values of thickness of the temperature compensation layer 92, the values of thickness of the temperature compensation layer 92 formed of SiO₂ that optimize the Mode3 and Mode4 resonant frequencies were determined to be ( 3/64)λ, and ( 1/32)λ, respectively. However, these thickness values are not to be construed in a limiting sense since the thickness of the temperature compensation layer 92 formed of SiO₂ may be any suitable and/or desirably thickness such as, without limitation, ≤1λ, ≤(½)λ, ≤(⅜)λ, ≤(¼)λ, or ≤(⅛)λ.

Second Example UBAR: A Device-Layer-Enabled Mode3 and or Mode4 Resonance without the Presence of a Temperature-Compensation Layer

In some non-limiting embodiments or examples, for the purpose of comparison and/or modeling, the frequency response was determined for a frequency sweep (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to a second example UBAR 2 which is similar in most respects to the first example UBAR 2 (shown in FIG. 1) described above with the exception that the second example UBAR 2 excludes temperature compensation layer 92. A plot, graph, or relationship of frequency vs. amplitude was determined for the frequency sweep.

Utilizing equations EQ1 and EQ2 and the plot, graph, or relationship of frequency vs. amplitude determined for the frequency sweep, the coupling efficiencies M3CE and M4CE for the Mode3 and Mode4 resonant frequencies 86 and 88 of the second example UBAR 2 were determined to be:

M3CE=40.093%—for values of f_(p1) and f_(s1) equal to 3.738 GHz and 3.13 GHz, respectively; and

M4CE=9.312%—for values of f_(p2) and f_(s2) equal to 6.194 GHz and 5.96 GHz, respectively.

However, the foregoing value of M3CE in this example is not to be construed in a limiting sense since a value of M3CE ≥8%, ≥11%, ≥14%, ≥17%, or ≥20% may be satisfactory, suitable, and/or desirable. Also or alternatively, the foregoing value of M4CE in this example is not to be construed in a limiting sense since a value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be satisfactory, suitable, and/or desirable.

In some non-limiting embodiments or examples, when a specific value of M3CE, for example, ≥8%, ≥11%, ≥14%, ≥17%, or ≥20%, is desired, the cut angle of piezoelectric layer 8 may extend beyond the above cut angle of 0° (or 180°)±20°, e.g., a cut angle of 0° (or 180°)≥±20°, ≥±30°, ≥±40°, ≥±50°, etc. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M3CE.

In some non-limiting embodiments or examples, when a certain level of M4CE, for example, ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, is desired, the cut angle of piezoelectric layer 8 may extend beyond a cut angle of 130°±30° (sometimes called a Y-Cut130±30 or a YX-cut130±30), e.g., a cut angle of 130°≥±30°, ≥±40°, ≥±50°, etc. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M4CE.

As can be understood from the values of M4CE for UBAR 2 with and without the temperature compensation layer 92 described above, the coupling efficiency may be greater for UBAR 2 with the temperature compensation layer 92 of SiO₂ and, conversely, the coupling efficiency may be less for UBAR 2 without the temperature compensation layer 92 of SiO₂. In some non-limiting embodiments or examples, generally, a greater value of coupling efficiency is more desirable.

Third Example UBAR: A Device-Layer-Enabled Mode3 and or Mode4 Resonance with the Presence of a Temperature-Compensation Layer and a Layer of Aluminum Nitride

With reference to FIG. 12 and with continuing reference to FIG. 11, in some non-limiting embodiments or examples, for the purpose of comparison and/or modeling, the frequency response was determined for a frequency sweep (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to a third example UBAR 2 (shown in FIG. 12) which is similar in most respects to the first example UBAR 2 described above with at least the following exceptions: namely, the third example UBAR 2 includes a layer of AlN 96 between the device layer 12 of diamond or SiC and the temperature compensation layer 92 of SiO₂ shown atop of AlN layer 96 in FIG. 12, AlN layer 96 has a thickness of ( 7/16)λ, the temperature compensation layer 92 of SiO₂ has a thickness of ( 11/128)λ, and the device layer 12 formed of diamond or SiC has a thickness (90/16)λ. In this example, λ is equal to 1.6 μm. A plot, graph, or relationship of frequency vs. amplitude was determined for the frequency sweep.

Utilizing equations EQ1 and EQ2 and the plot, graph, or relationship of frequency vs. amplitude determined for the frequency sweep, the coupling efficiencies M3CE and M4CE for the Mode3 and Mode4 resonant frequencies 86 and 88 of the third example UBAR 2 shown in FIG. 12 were determined to be:

M3CE=39.351%—for values of f_(p1) and f_(s1) equal to 3.608 GHz and 3.032 GHz, respectively; and

M4CE=10.802%—for values of f_(p2) and f_(s2) equal to 5.02 GHz and 4.8 GHz, respectively.

However, the foregoing value of M3CE in this example is not to be construed in a limiting sense since a value of M3CE ≥8%, ≥11%, ≥14%, ≥17%, or ≥20% may be satisfactory, suitable, and/or desirable. Also or alternatively, the foregoing value of M4CE in this example is not to be construed in a limiting sense since a value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be satisfactory, suitable, and/or desirable.

In some non-limiting embodiments or examples, when a specific value of M3CE, for example, ≥8%, ≥11%, ≥14%, ≥17%, or ≥20%, is desired, the cut angle of piezoelectric layer 8 may extend beyond the above cut angle of 0° (or 180°)±20°, e.g., a cut angle of 0° (or 180°)≥±20°, ≥±30°, ≥±40°, ≥±50°, etc. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M3CE.

In some non-limiting embodiments or examples, when a certain level of M4CE, for example, ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, is desired, the cut angle of piezoelectric layer 8 may extend beyond a cut angle of 130°±30° (sometimes called a Y-Cut130±30 or a YX-cut130±30), e.g., a cut angle of 130°≥±30°, ≥±40°, ≥±50°, etc. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M4CE.

In the above examples of first through third example UBARs, M3CE and M4CE were determined for piezoelectric layer 8 formed of a crystal of LiNbO₃ cut at an angle of 0° (or 180°). In some non-limiting embodiments or examples, applicants have discovered that a piezoelectric layer 8 formed of a crystal of LiNbO₃ cut at an angle of about 130° (sometimes called an YX-Cut130°, or a Y-Cut130°) can improve or optimize the coupling efficiency M4CE of the Mode4 resonant frequency 88. In an example, the cut angle of the piezoelectric layer 8 formed of a crystal of LiNbO₃ can be 130°±30°, e.g., in a range between 100° and 160°; more preferably 130°±20°, e.g., in a range between 110° and 150°; and most preferably 130°±10°, e.g., in a range between 120° and 140°. However, these ±values or ranges are not to be construed in a limiting sense.

Moreover, in some non-limiting embodiments or examples, applicants have discovered that a UBAR 2 formed with alternating layers of low and high acoustic impedance materials between the piezoelectric layer 8 (formed of a crystal of LiNbO₃ cut at an angle of about 130° (±30°, or ±20°, or ±10°)) and the device layer 12 (when substrate 16 is omitted) or the substrate 16 (when device layer 12 is omitted), or both device layer 12 and substrate 16 when both are present, can also improve or optimize the coupling efficiency M4CE of the Mode4 resonant frequency 88. In some non-limiting embodiments or examples, UBAR 2 formed with alternating layers of low and high acoustic impedance materials can include device layer 12 formed of diamond, SiC, W, Ir, or AlN and substrate 16 formed of silicon. In some non-limiting embodiments or examples, UBAR 2 formed with alternating layers of low and high acoustic impedance materials can include substrate 16 formed of silicon, but can exclude device layer 12.

Fourth Example UBAR: A Flexural Mode (Mode4) Enabled by a Stack Comprising at Least a Low Acoustic Impedance Layer and a High Acoustic Impedance Layer and, Optionally, with a Device Layer

With reference to FIG. 13 and with continuing reference to FIG. 11, in some non-limiting embodiments or examples, a fourth example UBAR 2 (shown in FIG. 13) formed of alternating layers of low and high acoustic impedance materials can include, from piezoelectric layer 8 (formed of a crystal of LiNbO₃ cut at an angle of about 130° (±30°, or ±20°, or ±10°)) to (optional) device layer 12 or substrate 16, a first low acoustic impedance layer 100, a first high acoustic impedance layer 102, a second low acoustic impedance layer 104, a second high acoustic impedance layer 106, and a third low acoustic impedance layer 108. In this example, the finger pitch 38 of the spaced conductive lines or fingers 20 or 28 (shown in FIGS. 4A-4B) of top electrode 6 is 1.2 μm, the value of λ is 2.4 μm, the thickness of piezoelectric layer is λ/2, the thickness of device layer 12, when present, is 4λ, and the thickness of substrate 16 is 20 μm. In this example, for the purpose of modeling, the cut angle of piezoelectric layer 8 was varied between 100° and 160°.

In some non-limiting embodiments or examples, each low acoustic impedance layer 100, 104, and 108 can be formed of silicon dioxide (SiO₂), each high acoustic impedance layer 102 and 106 can be formed of a metal, such as, for example, tungsten (W), device layer 10 can be formed of diamond or SiC, and substrate 16 can be formed of silicon. In an example, device layer 12 can be optional, whereupon third low acoustic impedance layer 108 can be in direct contact with substrate 12 and second high acoustic impedance layer 106.

In some non-limiting embodiments or examples, for the purpose of modeling, frequency responses (frequency vs. amplitude) were determined for frequency sweeps (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to a number of fourth example UBARs 2, with and without device layer 12, for each of a number of different cut angles of piezoelectric layer 8 varied between 100° and 160°, for each of a number of different exemplary values of thicknesses of low acoustic impedance layers 100, 104, and 108, and for each of a number of different exemplary values of thicknesses of high acoustic impedance layers 102 and 106, e.g., in the manner described above for the first example UBAR 2. In other words, frequency responses (frequency vs. amplitude) were determined for frequency sweeps (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to a number of fourth example UBARs 2 having different combinations of: (1) device layer 12 or no device layer 12; (2) cut angles of piezoelectric layer 8 varied between 100° and 160°; (3) values of thicknesses of low acoustic impedance layers 100, 104, and 108, and (4) values of thicknesses of high acoustic impedance layers 102 and 106.

In some non-limiting embodiments or examples, for each cut angle of piezoelectric layer 8, the thickness of each low acoustic impedance layer 100, 104, and 108 was set to the same (first) value and the thickness of each high acoustic impedance layer 102 and 106 was set to the same (second) value, a frequency of the exemplary electrical stimulus applied to the fourth example UBAR 2 was swept from, for example, 1 GHz to 6.2 GHz, and the frequency response of the fourth example UBAR 2 for said sweep was recorded. Then, the value of only the thickness of the low acoustic impedance layers (the first value) or the value of thickness of the high acoustic impedance layer (the second value) was changed, the frequency sweep was repeated, and the frequency response of the fourth example UBAR 2 was recorded. This process was repeated for a number of different thickness values of low acoustic impedance layers and high acoustic impedance layers to characterize the frequency response of the fourth example UBAR 2 for different values of thicknesses of low acoustic impedance layers and high acoustic impedance layers. In some non-limiting embodiments or examples, the thickness of each low acoustic impedance layer and/or each high acoustic impedance layer may be the same or different. In some non-limiting embodiments or examples, diamond, SiC, W, Ir, AlN, etc., may be used a high acoustic impedance material. A plot, graph, or relationship of frequency vs. amplitude was determined for each frequency sweep.

Utilizing equation EQ2 and the plots, graphs, or relationships of frequency vs. amplitude determined for frequency sweeps of the fourth example UBAR 2, the optimal coupling efficiency M4CE for the Mode4 resonant frequencies 88 of the fourth example UBAR 2 shown in FIG. 13, with and without device layer 12, was determined to be:

M4CE=15.888%—for values of f_(p2) and f_(s2) equal to 5.43 GHz and 5.08 GHz, respectively,

for piezoelectric layer 8 having cut at an angle of, for example, 130°, and for a thickness of each low acoustic impedance layer 100, 104, and 108, for example, equal to ( 1/16)λ and a thickness of each high acoustic impedance layer 102 and 106, for example, equal to ( 1/16)λ.

The foregoing value of M4CE in this example is not to be construed in a limiting sense since a value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10% may be satisfactory, suitable, and/or desirable. In an example, the value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be achieved by adjusting the cut angle of piezoelectric layer 8 by ±a suitable and/or desirable value, e.g., 130°±30°, as described above. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M4CE.

Moreover, the foregoing thickness of each low acoustic impedance layer and/or each high acoustic impedance layer is/are not to be construed in a limiting sense since the thickness of each low acoustic impedance layer and/or the thickness of each high acoustic impedance layer may be any suitable and/or desirably thickness such as, without limitation, ≤1λ, ≤(½)λ, ≤(⅜)λ, ≤(¼)λ, or ≤(⅛)λ, and the thickness of each low and/or high acoustic impedance layer may be different (or the same) as the thickness of any other low and/or high acoustic impedance layer. Accordingly, herein, the thicknesses of low acoustic impedance layers being the same, the thicknesses of high acoustic impedance layers being the same, or the thicknesses of low acoustic impedance layer(s) being the same as the thickness of high acoustic impedance layer(s) is not to be construed in a limiting sense.

Fifth Example UBAR: A Flexural Mode (Mode4) Enabled by a Stack Comprising at Least a Low Acoustic Impedance Layer and a High Acoustic Impedance Layer and, Optionally, with a Device Layer

With continuing reference to FIGS. 11 and 13, in some non-limiting embodiments or examples, in a manner similar to the fourth example UBAR 2 described above, for each of a number of different cut angles of piezoelectric layer 8 between 100° and 160°, for the purpose of modeling, frequency responses (frequency vs. amplitude) were determined for frequency sweeps (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to different thickness values of low acoustic impedance layers and high acoustic impedance layers of a fifth example UBAR 2 which is similar in most respects to the fourth example UBAR 2 (shown in FIG. 13) described above with the following exception: namely, low acoustic impedance layer 108 is omitted. A plot, graph, or relationship of frequency vs. amplitude was determined for each frequency sweep.

Utilizing equation EQ2 and the plots, graphs, or relationships of frequency vs. amplitude determined for the fifth example UBAR 2, the optimal coupling efficiency M4CE for the Mode4 resonant frequencies 88 of the fifth example UBAR 2, with and without device layer 12, were determined to be same as the fourth example UBAR 2, namely:

M4CE=15.888%—for values of f_(p2) and f_(s2) equal to 5.43 GHz and 5.08 GHz, respectively,

for piezoelectric layer 8 having cut at an angle of 130°, and for a thickness of each low acoustic impedance layer 100 and 104 equal to ( 1/16)λ and a thickness of each high acoustic impedance layer 102 and 106 equal to ( 1/16)λ.

In some non-limiting embodiments or examples, the thickness of each low acoustic impedance layer and/or each high acoustic impedance layer may be the same or different. In some non-limiting embodiments or examples, diamond, SiC, W, AlN, Ir, etc., may be used as the material for each high acoustic impedance layer.

The foregoing value of M4CE in this example is not to be construed in a limiting sense since a value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10% may be satisfactory, suitable, and/or desirable. In an example, the value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be achieved by adjusting the cut angle of piezoelectric layer 8 by ±a suitable and/or desirable value, e.g., 130°±30°, as described above. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M4CE.

Moreover, the foregoing thickness of each low acoustic impedance layer and/or each high acoustic impedance layer is/are not to be construed in a limiting sense since the thickness of each low acoustic impedance layer and/or the thickness of each high acoustic impedance layer may be any suitable and/or desirably thickness such as, without limitation, ≤1λ, ≤(½)λ, ≤(⅜)λ, ≤(¼)λ, or ≤(⅛)λ, and the thickness of each low and/or high acoustic impedance layer may be different (or the same) as the thickness of any other low and/or high acoustic impedance layer. Accordingly, herein, the thicknesses of low acoustic impedance layers being the same, the thicknesses of high acoustic impedance layers being the same, or the thicknesses of low acoustic impedance layer(s) being the same as the thickness of high acoustic impedance layer(s) is not to be construed in a limiting sense.

This result suggests that there may be little if any additional benefit of having one or more additional low acoustic impedance layers between high acoustic impedance layer 106 and device layer 12, or substrate 16, or both.

Sixth Example UBAR: A Flexural Mode (Mode4) Enabled by a Stack Comprising at Least a Low Acoustic Impedance Layer and a High Acoustic Impedance Layer and, Optionally, with a Device Layer

With reference to FIG. 14 and with continuing reference to FIG. 11, in some non-limiting embodiments or examples, a sixth example UBAR 2 (shown in FIG. 14) formed of alternating layers of low and high acoustic impedance materials can include, from piezoelectric layer 8 (formed of a crystal of LiNbO₃ cut at an angle of about 130° (±30°, or ±20°, or ±10°)) to device layer 12: first low acoustic impedance layer 100, first high acoustic impedance layer 102, second low acoustic impedance layer 104, second high acoustic impedance layer 106, third low acoustic impedance layer 108, third high acoustic impedance layer 110, fourth low acoustic impedance layer 112. fourth high acoustic impedance layer 114, fifth low acoustic impedance layer 116, fifth high acoustic impedance layer 118, sixth low acoustic impedance layer 120, sixth high acoustic impedance layer 122, seventh low acoustic impedance layer 124, seventh high acoustic impedance layer 126, eighth low acoustic impedance layer 128, eighth high acoustic impedance layer 130, and ninth low acoustic impedance layer 132.

In this example, the finger pitch 38 of the spaced conductive lines or fingers 20 or 28 (shown in FIGS. 4A-4B) of top electrode 6 is 1.2 μm, the value of λ is 2.4 μm, the thickness of piezoelectric layer is (0.2)λ, the thickness of each low acoustic impedance layer is ( 1/16)λ, and the thickness of device layer 12 is 4λ.

For the purpose of modeling the sixth example UBAR 2 for each of a number of different cut angles of piezoelectric layer 8 between 100° and 160°, frequency responses were determined for frequency sweeps (for example, from 1 GHz to 6.2 GHz) of an exemplary electrical stimulus applied to the sixth example UBAR 2 for a number of different exemplary values of thickness of the high acoustic impedance layers in the manner described above for the fourth example UBAR 2. In this example, for each cut angle of piezoelectric layer 8 and each frequency sweep, each high acoustic impedance layer has the same thickness value. A plot, graph, or relationship of frequency vs. amplitude was determined for each frequency sweep.

In some non-limiting embodiments or examples, each low acoustic impedance layer can be formed of silicon dioxide (SiO₂), each high acoustic impedance layer can be formed of, for example, Aluminum Nitride (AlN), device layer 10 can be formed of diamond or SiC, and substrate 16 can be formed of silicon.

Utilizing equation EQ2 and the plots, graphs, or relationships of the frequency responses determined for the sixth example UBAR 2, the optimal coupling efficiency M4CE for the Mode4 resonant frequency 88 of the sixth example UBAR 2 was determined to be:

M4CE=13.287%—for values of f_(p2) and f_(s2) equal to 5.38 GHz and 5.09 GHz, respectively,

for piezoelectric layer 8 having cut at an angle of 130° and for a thickness of each high acoustic impedance layer equal to ( 5/16)λ.

In some non-limiting embodiments or examples, the thickness of each low acoustic impedance layer and/or that of each high acoustic impedance layer may be the same or different. In some non-limiting embodiments or examples, diamond, SiC, W, AlN, etc., may be used as the material for each high acoustic impedance layer.

The foregoing value of M4CE in this example is not to be construed in a limiting sense since a value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be satisfactory, suitable, and/or desirable. Moreover, the foregoing thickness of each low acoustic impedance layer and/or each high acoustic impedance layer is/are not to be construed in a limiting sense since the thickness of each low acoustic impedance layer and/or the thickness of each high acoustic impedance layer may be any suitable and/or desirably thickness such as, without limitation, ≤1λ, ≤(½)λ, ≤(⅜)λ, ≤(¼)λ, or ≤(⅛)λ, and the thickness of each low and/or high acoustic impedance layer may be different (or the same) as the thickness of any other low and/or high acoustic impedance layer. Accordingly, herein, the thicknesses of low acoustic impedance layers being the same, the thicknesses of high acoustic impedance layers being the same, or the thicknesses of low acoustic impedance layer(s) being the same as the thickness of high acoustic impedance layer(s) is not to be construed in a limiting sense.

In an example, the value of M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%, may be achieved by adjusting the cut angle of piezoelectric layer 8 by ±a suitable and/or desirable value, e.g., 130°±30°, as described above. In some non-limiting embodiments or examples, piezoelectric layer 8, such as, without limitation, an LiNbO₃ crystal, produced from a desired cut angle of a Z-Cut or an X-Cut may also be sufficient to obtain the desired specific value of M4CE.

In some non-limiting embodiments or examples, the modeling of the first through sixth example UBARs 2 described above were performed by computer simulation and, in some instances, on one or more physical samples.

In some non-limiting embodiments or examples, it was determined from the models of the first through sixth example UBARs 2 described above, that piezoelectric layer 8 formed of LiNbO₃ cut at an angle at or about 130° optimized the value of M4CE. However, in some non-limiting embodiments or examples, it was also determined that piezoelectric layer 8 formed of LiNbO₃ cut at an angle of between 100° and 160° also produced desirable values of M4CE; while piezoelectric layer 8 formed of LiNbO₃ cut at an angle of between 110° and 150° produced more desirable values of M4CE; and piezoelectric layer 8 formed of LiNbO₃ cut at an angle of between 120° and 140° produced even more desirable values of M4CE. However, piezoelectric layer 8 formed of LiNbO₃ cut at an angle of 130° produced a most desirable (highest) value of M4CE.

In any example UBAR described herein, the thickness of piezoelectric layer, such as LiNbO₃, may be any suitable and/or desirable thickness, such as, in an example, ≤0.5λ, ≤0.4λ, ≤0.3λ, or ≤0.2λ for flexural mode—Mode4.

In any example UBAR described herein, the thickness of piezoelectric layer, such as LiNbO₃, may be any suitable and/or desirable thickness, such as, in an example, ≤2λ, ≤1.6λ, ≤1.2λ, or ≤0.8λ for shear mode—Mode3.

In any example UBAR described herein, the thickness of an electrode, for example, Al, Mo, W, etc., may be any suitable and/or desirable thickness, such as, in an example, ≥0.010λ, ≥0.013λ, ≥0.016λ, ≥0.019λ, or ≥0.022λ.

In any example UBAR described herein, the thickness of a device layer, for example, diamond, SiC, AlN, etc., may be any suitable and/or desirable thickness, such as, in an example, ≥50 nm, ≥100 nm, ≥150 nm, or ≥200 nm.

In any example UBAR described herein, the thickness of a low acoustic impedance layer may be any suitable and/or desirable thickness, such as, in an example, ≥0.05λ, ≥0.07λ, ≥0.09λ, ≥0.11λ, or ≥0.13λ.

In any example UBAR described herein, the thickness of a high acoustic impedance layer may be any suitable and/or desirable thickness, such as, in an example, ≥0.05λ, ≥0.07λ, ≥0.09λ, ≥0.11λ, or ≥0.13λ.

In any example UBAR described herein, the thickness of a temperature compensation layer in may be any suitable and/or desirable thickness, such as, in an example, ≤2λ, ≤1.5λ, ≤1.0λ, ≤0.5λ, or ≤0.3λ. Optionally, one or more or all exterior surfaces of any example UBAR described herein may be protected by an optional passivation layer. The passivation may be a layer of dielectric material, for example, AlN, SiN, SiO₂, etc.

The resonant frequency of any example UBAR described herein may be ≥0.1 GHz, ≥0.5 GHz, ≥1.0 GHz, ≥1.5 GHz, or ≥2.0 GHz.

The coupling efficiency of any example UBAR described herein may be ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%.

Any example UBAR described herein may resonate in a mode comprising a bulk acoustic wave, a shallow bulk acoustic wave which may include, but not be limited to, S₀ mode, extensional mode, shear mode, A1 mode, flexural mode, etc., and a composite mode.

Further non-limiting embodiments or examples are set forth in the following numbered clauses.

Clause 1: A bulk acoustic resonator comprises: a resonator body including: a piezoelectric layer, wherein the piezoelectric layer is a single crystal of LiNbO₃; a device layer; and a top conductive layer on the piezoelectric layer opposite the device layer, wherein substantially all of a surface of the device layer opposite the piezoelectric layer is for mounting the resonator body to a carrier that is not part of the resonator body.

Clause 2: The bulk acoustic resonator of clause 1, wherein the single crystal of LiNbO₃ can be cut at an angle of 130°±30°, ±20°, or ±10°.

Clause 3: The bulk acoustic resonator of clause 1 or 2, wherein the single crystal of LiNbO₃ can be cut at an angle of 0°±30°, ±20°, or ±10°.

Clause 4: The bulk acoustic resonator of any one of clauses 1-3 may include a Mode3 or a Mode 4 resonance at a frequency ≥0.1 GHz, ≥0.5 GHz, ≥1.0 GHz, ≥1.5 GHz, or ≥2.0 GHz.

Clause 5: The bulk acoustic resonator of any one of clauses 1-4, may comprise at least one of the following: a Mode3 resonance having a coupling efficiency ≥8%, ≥11%, ≥14%, ≥17%, or ≥20%; and a Mode4 resonance having a coupling efficiency ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%.

Clause 6: The bulk acoustic resonator of any one of clauses 1-5, wherein, for Mode4 resonance, the single crystal of LiNbO₃ may have a thickness ≤0.5λ, ≤0.4λ, ≤0.3λ, or ≤0.2λ.

Clause 7: The bulk acoustic resonator of any one of clauses 1-6, wherein, for Mode3 resonance, the single crystal of LiNbO₃ may have a thickness ≤2λ, ≤1.6λ, ≤1.2λ, or ≤0.8λ.

Clause 8: The bulk acoustic resonator of any one of clauses 1-7 may further include between the piezoelectric layer and the device layer a conductive layer having a thickness ≥0.010λ, ≥0.013λ, ≥0.016λ, ≥0.019λ, or ≥0.022λ.

Clause 9: The bulk acoustic resonator of any one of clauses 1-8, wherein the device layer may have a thickness ≥50 nm, ≥100 nm, ≥150 nm, or ≥200 nm.

Clause 10: The bulk acoustic resonator of any one of clauses 1-9 may further include between the piezoelectric layer and the device layer a layer of low acoustic impedance material having an acoustic impedance between 10⁶ Pa-s/m³ and 30×10⁶ Pa-s/m³ and a thickness ≥0.05λ, ≥0.07λ, ≥0.09λ, ≥0.11λ, or ≥0.13λ.

Clause 11: The bulk acoustic resonator of any one of clauses 1-10 may further include between the piezoelectric layer and the device layer a layer of high acoustic impedance material having an acoustic impedance between 10⁶ Pa-s/m³ and 630×10⁶ Pa-s/m³ and a thickness ≥0.05λ, ≥0.07λ, ≥0.09λ, ≥0.11λ, or ≥0.13λ.

Clause 12: The bulk acoustic resonator of any one of clauses 1-11 may further include between the piezoelectric layer and the device layer a temperature compensation layer comprising Si and oxygen having a thickness ≤2λ, ≤1.5λ, ≤1.0λ, ≤0.5λ, or ≤0.3λ.

Clause 13: The bulk acoustic resonator of any one of clauses 1-12 may further include a passivation layer.

Clause 14: The bulk acoustic resonator of any one of clauses 1-13, wherein the top conductive layer may include at least one pair of spaced conductive fingers. The at least one pair of spaced conductive fingers may have a finger pitch ≤70 μm, ≤20 μm≤10 μm, ≤6 μm, or ≤4 μm.

Clause 15: The bulk acoustic resonator of any one of clauses 1-14 may further include between the piezoelectric layer and the device layer plural alternating temperature compensation layers and high acoustic impedance layers.

Clause 16: The bulk acoustic resonator of any one of clauses 1-15, wherein the device layer may comprise at least one of the following: diamond; W; SiC; Ir, AlN, Al; Pt; Pd; Mo; Cr; Ti; Ta; an element from Group 3A or 4A of the periodic table of the elements; a transition element from Group 1B, 2B, 3B, 4B, 5B, 6B, 7B, or 8B of the periodic table of the elements; ceramic; glass; and polymer.

Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical preferred and non-limiting embodiments, examples, or aspects, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed preferred and non-limiting embodiments, examples, or aspects, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any preferred and non-limiting embodiment, example, aspect, or the appended claim can be combined with one or more features of any other preferred and non-limiting embodiment, example, aspect, or the appended claim. 

The invention claimed is:
 1. A bulk acoustic resonator comprising: a resonator body including: a piezoelectric layer, wherein the piezoelectric layer is a single crystal of LiNbO₃; a device layer; and a top conductive layer on the piezoelectric layer opposite the device layer, wherein substantially all of a surface of the device layer opposite the piezoelectric layer is for mounting the resonator body to a carrier that is not part of the resonator body.
 2. The bulk acoustic resonator of claim 1, wherein the single crystal of LiNbO₃ is cut at an angle of 130°±30°.
 3. The bulk acoustic resonator of claim 1, wherein the single crystal of LiNbO₃ is cut at an angle of 130°±20°.
 4. The bulk acoustic resonator of claim 1, wherein the single crystal of LiNbO₃ is cut at an angle of 130°±10°.
 5. The bulk acoustic resonator of claim 1, wherein the single crystal of LiNbO₃ is cut at an angle of 0°±30°.
 6. The bulk acoustic resonator of claim 1, wherein the single crystal of LiNbO₃ is cut at an angle of 0°±20°.
 7. The bulk acoustic resonator of claim 1, wherein the single crystal of LiNbO₃ is cut at an angle of 0°±10°.
 8. The bulk acoustic resonator of claim 7, including a Mode3 or a Mode 4 resonance at a frequency ≥0.1 GHz.
 9. The bulk acoustic resonator of claim 1, comprising at least one of the following: a Mode3 resonance having a coupling efficiency ≥8%; and a Mode4 resonance having a coupling efficiency ≥3%.
 10. The bulk acoustic resonator of claim 9, wherein, for Mode4 resonance, the single crystal of LiNbO₃ has a thickness ≤0.5λ, wherein a value of λ is based on a dimension of a pattern or feature defined by top conductive layer or based on a thickness of the single crystal of LiNbO₃.
 11. The bulk acoustic resonator of claim 9, wherein, for Mode3 resonance, the single crystal of LiNbO₃ has a thickness ≤2λ, wherein a value of λ is based on a dimension of a pattern or feature defined by top conductive layer or based on a thickness of the single crystal of LiNbO₃.
 12. The bulk acoustic resonator of claim 1, further including between the piezoelectric layer and the device layer a conductive layer having a thickness ≥0.010λ, wherein a value of λ is based on a dimension of a pattern or feature defined by top conductive layer or based on a thickness of the single crystal of LiNbO₃.
 13. The bulk acoustic resonator of claim 1, wherein the device layer has a thickness ≥50 nm.
 14. The bulk acoustic resonator of claim 1, further including between the piezoelectric layer and the device layer a layer of low acoustic impedance material having an acoustic impedance between 10⁶ Pa-s/m³ and 30×10⁶ Pa-s/m³ and a thickness ≥0.05λ, wherein a value of λ is based on a dimension of a pattern or feature defined by top conductive layer or based on a thickness of the single crystal of LiNbO₃.
 15. The bulk acoustic resonator of claim 1, further including between the piezoelectric layer and the device layer a layer of high acoustic impedance material having an acoustic impedance between 10⁶ Pa-s/m³ and 630×10⁶ Pa-s/m³ and a thickness ≥0.05λ, wherein a value of λ is based on a dimension of a pattern or feature defined by top conductive layer or based on a thickness of the single crystal of LiNbO₃.
 16. The bulk acoustic resonator of claim 1, further including between the piezoelectric layer and the device layer a temperature compensation layer comprising Si and oxygen having a thickness ≤2λ, wherein a value of λ is based on a dimension of a pattern or feature defined by top conductive layer or based on a thickness of the single crystal of LiNbO₃.
 17. The bulk acoustic resonator of claim 1, further including a passivation layer.
 18. The bulk acoustic resonator of claim 1, wherein the top conductive layer includes at least one pair of spaced conductive fingers.
 19. The bulk acoustic resonator of claim 1, further including between the piezoelectric layer and the device layer plural alternating temperature compensation layers and high acoustic impedance layers.
 20. The bulk acoustic resonator of claim 1, wherein the device layer comprises at least one of the following: diamond; W; SiC; Ir, AlN, Al; Pt; Pd; Mo; Cr; Ti; Ta; an element from Group 3A or 4A of the periodic table of the elements; a transition element from Group 1B, 2B, 3B, 4B, 5B, 6B, 7B, or 8B of the periodic table of the elements; ceramic; glass; and polymer. 